How does the OMP system work ?
 

Today I had a discussion with a friend about how the OMP system is working and we both couldnt agree. I have a pretty good idea of how I think it is supposed to work because I ve seen an engine or two :nod:
Let me first say that the FSM does not explain how it is supposed to work, it just states how to troubleshoot. So thats why I am opening this thread, so If you have the answer I am glad to hear it.

How I think it is supposed to work:
So the OMP consists of a pump, 4 nozzels, 4 lines and some vacuum lines.
1 nozzle per rotor housing and one nozzle per primary intake runner. Making a total of 4 nozzels for a 13B. Easy going.
Each of these nozzels is connected with 2 lines. One is fitted banjo style and goes to the OMP pump on the front cover.
The other one is on top of the nozzle and goes to a vacuum splitter (spider) which leads to the intake throttle body. Easy too.

After performing a test on a running engine (S4 NA) I can tell that the vacuum line that connects to the intake is under vacuum, I pulled it on the TB and if I put my finger on the rubber line I can feel vacuum.
So basically when looking at the nozzle it has a longtitual bore from top to bottom, perpendicular it has another bore where the OMP line connects.
After this test I am able to say that the longtitual bore enables the nozzle to pull negative pressure (vacuum) through it, as NAs have negative pressure on the intake manifold :) . I am sure, I tested it.
It does pull vacuum and the engine is running like shit if its not connected, but if I place my finger on it, the engine runs fine. :icon_tup:
The OMP pump is connected via tooth gear to the eshaft and does spin at a certain ratio (That I dont know) of the engines rpm, most likely pumping oil from the oil pan through the OMP lines (as a pump is supposed to do).
If I interpreted the FSM right it is about 1 ccm max per minute at 2000 rpm with pump lever and 2 omp lines disconnected and lever pulled upwards on "Full throttle" position.
So I think it is safe to assume that the pump does not have a lot of pressure and oil is merely dripping out of the line instead of squirting like an injector for example.

So if I did follow my highschool physics right, Bernoullis law says that If I have a tube from which I am pulling air on one end, airflow establishes. That was easy. :)
If I add a bore somewhere on the tube, air is being pulled through that bore into the tube due to air passing by on the inside and creating a low pressure area on the hole.
So replace the tube mentionned with an OMP nozzle and the added bore as the OMP line feed, we have a system that does suck oil droplets out of the line by using the Bernoulli effect and pulls them downstream into the intake or housing.
On the bottomside of the OMP nozzle the bore gets reaaaally tight. So following the Bernoullis law, fluid speeds increase when reducing tube diameter,
I think its safe to assume that the oil droplets will get atomized pretty damn good when they come out at the bottom :nod: I think thats what they call the Venturi effect.

I think that system is pretty damn simple and awesome if you ask me :icon_tup:
After feeling that there is vacuum on the rubber line that comes from the nozzles top and goes to the TB it took me 5 seconds to come to the above conclusion. As I said I was amazed, but my friend does not share my thoughts.

What I found out afterwards:
Inspecting one of my OMP nozzles I found out the longtitual bore has a check valve and allows only airflow from top to bottom. But that does not affect my thoughts on how its working.
Just making sure air can only pass in one direction: Top to bottom.

As said, please let me know what you think about it. :scratch: I could be completly wrong, but I am sure my conclusion is right on the spot. :blush:

Many thanks
Steven

Your explanation is consistent with my (limited) understanding of the system, for whatever that's worth.

Many thanks for your reply. Sounds about logic to me. To be honest I think its a great system. Very simple and very effective. :icon_tup: I will keep it for sure :)
Lets wait on input from others. If I am right we might make it sticky after I went through all the trouble of typing lol :)

Steven

although I applaud you for the extensive write up,it leaves me with this question.
Doesn't anyone just Drive these cars anymore?..(chuckle!)

I send the link to my friend so I dont have to type it twice. Sorry for that long text :)
Initially I was thinking the airflow would be the other way round, and seeing the omp nozzles that didn't make sense and I was stuck, until I did that test yesterday. Doh, than it made sense :nod:

I do.

,

I Just looked in the Training Manual in the lubrication section, and the one page the had on the oil nozzles corroborates your deductions.

FWIW. You should easily be able to find the training manual online. Everyone who tinkers with these cars should have it and read it. It just helps you to fully understand the systems and why they were designed however which way. I find the section on the rear suspension geometry particularly fascinating.